For the record, I cannot argue intent. All I can do is provide my interpretation of the author's chosen words.
You are correct, Squeggs. I have often seen "canon" used to describe a body of work. For example, Confederacy of Dunces is part of the Southern literary canon. I believe the author describing the BB 60 is using "canonical" as an adjective. In other words, he is aware that 54 begat 60. He is using "canonical" as an allegory to interject a clear example of why this reasoning is invalid and weak. Otherwise the author would use 1st full, 1st cameo, or just plain 1st appearance of the Teen Titans.